Description of problem:
The nodes unittests print lots of errors to the screen when run in Python 2.6. The errors are of the form "Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2bc6950>> ignored".

Version-Release number of selected component (if applicable):
2.4.0-1

How reproducible:
Every time

Steps to Reproduce:
1. nosetests -sx nodes/test/unit

Actual results:
(pulp)[rbarlow@notepad]~/devel/pulp% nosetests -sx nodes/test/unit
.................................../home/rbarlow/devel/pulp/server/pulp/server/db/connection.py:140: DeprecationWarning: The safe parameter is deprecated. Please use write concern options instead.
  return method(*args, **kwargs)
.......................................................................Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2bc6950>> ignored
.Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2bc64d0>> ignored
.......Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2f62410>> ignored
.Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2f0d1d0>> ignored
.Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2da1c10>> ignored
.Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2f5a090>> ignored
.Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2dd7350>> ignored
.Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2dd9450>> ignored
.Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2f5ba10>> ignored
...........Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2f5a810>> ignored
....Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2f6c610>> ignored
.Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2f6c650>> ignored
.Exception AttributeError: "'NoneType' object has no attribute 'closed'" in <bound method UnitWriter.__del__ of <pulp_node.manifest.UnitWriter object at 0x2f6c750>> ignored

Expected results:
The above command should only print dots and the end of test report.